Kenya ranks 16th on the World Watch List, mainly due to Islamic extremism, and the level of violence perpetrated against Christians, particularly in the northeastern and coastal regions, is very high. AP Photo/ Gbemiga Olamikan

An Islamic extremist group has claimed responsibility for a deadly attack in northeastern Kenya that left six dead and dozens injured, saying it intentionally targeted Christians.

"We are behind the Mandera attack. During which, we killed six Christians," said Sheikh Abdiasis Musab, leader of Al-Shabab, an Islamic extremist group affiliated to al-Qaeda, the BBC reports.

The attack early on Thursday morning was targeted at a gated residential building mainly housing non-ethnic Somalis and non-Muslims, less than a mile from the Somalia border town of Beled Hawa. Al-Shabab said it carried out the attack, which left 27 people injured, because it wanted non-Muslims to leave what it regarded as Muslim areas.

During an interview with persecution watchdog Open Doors, one witness explained the attack: "The Al-Shabaab militants, wearing Kenyan army uniforms, entered the housing compound posing as Kenyan security officers on patrol. Once allowed in, they first attacked a mobile money transfer shop with an explosive device before throwing more explosives into the compound. The people were caught off-guard and shot as they tried to flee. They specifically targeted non-locals (those assumed to be Christians). Among the 6 dead is a local barber named Cege. Among the injured is an individual who hid in the ceiling, but the explosion from the grenades shook him, causing him to fall through the roof. He is currently in the hospital."

The attackers also reportedly planted landmines around the compound, one of which exploded as security officers tried to access the building.

"There are increased security personnel in town even as tension remains very high. Residents are declining interviews out of fear for their safety. Many have locked themselves in their homes," reported local workers.

Governor Ali Roba condemned the attack and vowed to defeat the terrorist group: "We have suffered yet another attack in Mandera and sadly we have lost six people," he said, according to The Guardian.

Al-Shabab, headquartered in Somalia, also killed 148 people in an attack on Kenya's north-eastern Garissa University College in April 2015. The militants reportedly singled out Christians and shot them, while freeing many Muslims.

Kenya ranks 16th on the World Watch List, mainly due to Islamic extremism, and the level of violence perpetrated against Christians, particularly in the northeastern and coastal regions, is very high, notes Open Doors.

"We are greatly saddened that this attack was targeted at people perceived, by militants, to be Christians. We ask that supporters pray for the people of Mandera. Pray for God's grace for family members of victims and local security forces as they bring the situation under control. There is a high level of fear among locals, and we pray that the Lord will strengthen His children as they, once more, bear the brunt of militant anger," an East Africa team member reported.